One method to operate an internal combustion engine having a turbocharger is presented in U.S. Pat. No. 5,845,495. This method presents a way to balance the output of two turbochargers that are in communication with different cylinder banks of a “V” engine. The method uses a pressure transducer to determine if a pressure differential exists between the engine's exhaust manifolds. If a pressure differential is present, the method can open a waste gate, deactivate fuel injection, or limit the throttle valve opening in an attempt to equalize cylinder backpressure.
The above-mentioned method can also have several disadvantages. For example, the method is not capable of compensating for cylinder charge variations that can occur when a single turbocharger is used to supply compressed air to two different cylinder banks. Since the method relies on making adjustments to the waste gates of two independent turbochargers, it is not capable of compensating for back pressure variations that may occur in single turbocharger applications. Further, in dual turbocharger applications, the method does not have the capacity to compensate for cylinder breathing differences that may occur between different cylinder banks. That is, the method simply adjusts cylinder back pressure without considering that the cylinder charge contents may also be different from cylinder bank to cylinder bank. For example, differences in valve timing between cylinder banks may result in a condition where the cylinder back pressure between two cylinder banks is nearly equal; however, the cylinders of one cylinder bank may be inducting more fresh air than the other cylinder bank. Consequently, there may be a torque imbalance between the two cylinder banks.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method to control an engine having variable event valve operation and a turbocharger.